Thank you very much AYamshanov !! Now contact OVH support to see where to configure the PTRs
When the solution is effective I share it here in case it happens to someone else
I have Plesk Onix with two IP and two sites, one IP for each site. One of the emails returns with the following error:
Diagnostic-Code: smtp; 550-"JunkMail rejected - ip206.ip-144-217-101.net
(procode.com.uy) 550-[144.217.101.206]:51978 is in an RBL on...